1. Field of the Invention
The present invention relates generally to spacers used to separate rotating parts particularly for a downhole gear box for a well pump. More specifically, the present invention relates to a multidirectional hydrodynamic spacer for use in fluid saturated environments.
2. Description of the Related Art
Spacers are commonly used to separate moving parts in machines. Spacers generally allow for the free movement of the various parts of a machine and tend to wear out due to the friction encountered in this task.
One particular application that uses spacers is a reducing gear in a downhole pump used in hydrocarbon production. Frequently the reducing gears will have spacers between the planet and the planet carrier to provide for free rotation of the planet relative to the carrier and to reduce wear on the planet and carrier. The planet gears in this application rotate in a bath of oil or some other lubricating fluid. The combination of a spacer and the lubricant can extend the life of the planet.
Hydrodynamic spacers are not known in the field because of the relatively high rotational speeds and the unidirectional nature of known hydrodynamic elements. Another field that uses similar technology is thrust bearings, as shown in U.S. Pat. Nos. 5,529,398 and 6,089,754. These bearings are shaped to use the fluid in their environment to separate one part from another. The advantage of this is that under ideal conditions the hydrodynamic bearing completely prevents any contact between the hard surfaces. A film of high pressure fluid is created between the solid surfaces. This greatly reduces wear and heat generation.
While each of the above referenced designs has its advantages, both use a series of ramps or guides aligned in a ring. As the bearing rotates, fluid travels over the ramps or guides and provides increased fluid pressure to maintain a film of oil between the bearing and some other part. Because the bearing is rotating, the ramps or guides are repeated in a ring formation about the bearing so that the fluid flows over one ramp or guide and then on to the next. One of the problems discussed in these patents is the natural migration of fluid to the outer diameter of the rotating bearing. As the bearing rotates at higher speeds centrifugal forces act on the fluid pressing it to the outer edges of the bearings. Another shortcoming of these bearing designs is that they are only efficient in one direction of rotation. When the direction of rotation is reversed the fluid flows over the ramps or guides in reverse and therefore does not build an effective barrier.
It would be advantageous to employ hydrodynamic bearings in a spacer application that operated efficiently in both directions, and was effective at high rotational speeds.
A hydrodynamic spacer or bearing for use in fluid filled environments is effective in either direction of rotation and takes full advantage of centrifugal forces exerted on the fluid. The spacer is comprised of a top side and a bottom side. The bottom side is shaped to mate with a planet or some other rotating element. The top side has a bearing surface, a pressure pocket and a pumping land, all concentrically located between an inner diameter and an outer diameter. The bearing surface extends from the outer diameter radially inward to a sharp containment edge. The pressure pocket is recessed relative to the bearing surface and extends radially inward from the containment edge to a sharp edge. The pumping land extends radially inward from the sharp edge to the inner diameter and is slightly recessed relative to the bearing surface while being elevated relative to the pressure pocket.
In operation the spacer will rotate at relatively high speeds, such that the nearby fluids will experience centrifugal forces. As centrifugal forces push oil from the inner diameter towards the outer diameter, they cross the pumping land and go over the sharp edge into the pressure pocket. Once in the pressure pocket, the fluids are maintained therein by the containment edge until the fluid pressure increases as the fluid passes over the containment edge and therefore over the bearing surface. As the fluid passes over the bearing surface, it is at an elevated pressure, thus separating the spacer from any element in contact with the bearing surface.